An editorial explanation of the distinction between security screening and an airline’s baggage allowance.
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A backpack is a normal form of cabin baggage. The important distinction is between screening what is inside it and deciding whether its size, weight and item count fit your airline booking. Passing a security checkpoint does not settle the airline’s baggage decision.
Delta’s published guidance, for example, includes a small backpack among personal-item options and separately explains its main carry-on dimensions. The same bag should not be assumed to qualify in both categories. A large travel backpack may be your main cabin bag, while a small daypack may occupy the personal-item allowance.
Pack so any item staff ask to inspect can be reached without dismantling the entire load. Keep toiletries grouped and electronic accessories from becoming a loose tangle around the computer. Follow the instructions at your actual screening lane; a bag advertised as convenient for screening does not determine those instructions.
Before leaving home, answer two separate questions: does the packed backpack meet the airline allowance, and are the things inside suitable for cabin travel under the applicable security and dangerous-goods rules? Treating those as separate checks is clearer than looking for a blanket approval attached to a backpack model.